This invention relates to monitors such as radars adapted to be carried on a vehicle for obtaining position data of a front-going vehicle by making use of wave motion such as radar light and more particularly to the technology of adjusting the position and orientation of the detection area of such a monitor or its optical axis herein referred to as the monitor axis.
Apparatus of the kind carried on a vehicle for monitoring front-going vehicles and obstacles or for cruise control are widely being developed and the kinds with a radar using electromagnetic waves or a laser are generally known. They are devices for transmitting electromagnetic waves or laser light to an object of detection within a specified detection area and measuring the distance to a target object from the delay of a reflected signal.
In the case of a laser radar, for example, a specified scan area is irradiated with laser light while scanning it usually in one direction such as the horizontal left-right direction, a timing for light emission is generated by a control circuit in order to measure a delay by reflected light, a counter is started with this timing, a laser diode (LD) is driven according to this timing for laser light emission, the timing of reception of reflected light over a threshold level is taken in by a signal processor and the delay is measured by stopping the counter. The direction of a target object of detection may also be determined from the timing of the laser light emission or the scan angle at the timing of the reception of the reflected light.
On the basis of the measured distance data to the target object, the direction data, the data on the quantity of received light and the data on the speed of the vehicle obtained from a speed sensor, the individual distance data are grouped together and correlated with the data obtained in the past such that the relative speed of the target object is calculated, the identity of the target object (a vehicle, a bicycle, a person, a display board or a roadside reflector?) is established and it is determined whether an alarm should be outputted or not.
Some devices for a vehicle for monitoring the distance between vehicles are provided with an image sensor such as a CCD camera (hereinafter simply referred to as a camera). This is for the purpose of catching the wave motion (usually visible light) from a specified detection area near the vehicle by means of the image sensor and analyzing and judging the presence or absence of a front-going vehicle and its position on the basis of the brightness distribution on the image of the detection area obtained from the signal on the received wave motion.
More recently, devices of the so-called fusion type using both a radar and a camera are coming to be investigated because a device of the fusion type can have its radar and camera to mutually complement the shortcomings of each other.
When a device of the fusion type is actually installed on a vehicle, if its actual detection area (the area from which reflected waves are actually received) is displaced from the ideal detection area (normally an area symmetrically extending in both horizontal directions from the forward direction of motion of the vehicle at a specified height), the reliability of the result of measurement is accordingly reduced. Thus, the work of adjusting the center position of the detection area (or the adjustment of the optical axis in the case of a laser radar) becomes necessary on the production line of the vehicle or at the inspection time at a repair factory in order to maintain the device in the condition without such a displacement.
Adjustment of the position and the orientation of the detection area is sometimes referred to as the axial adjustment. FIG. 15A shows an example of conventional method of axial adjustment in the direction perpendicular to the standard direction of scan (normally the vertical direction). According to this method, a standard reflector is set on the upper limit of what is considered to be a proper detection area for a laser radar installed on a stationary vehicle and the laser radar is activated after a condition is prepared such that there is no cause of external disturbance and no object other than this standard reflector would be detected. The elevation angle and the installed position of the laser radar are manually changed downward gradually and set manually when the reflector ceases to be detected.
FIG. 15B shows an example of conventional method of axial adjustment in the standard direction of the scan (usually the horizontal direction). According to this method, the reflector is positioned at the center of what is considered to be an optimum detection area for a laser radar installed on a stationary vehicle and the laser radar is activated after a condition is prepared such that there is no cause of external disturbance and no object other than this standard reflector would be detected. Next, the angle of installation may be physically changed manually such that the detected position of the reflector will match the center of the detection area or a software parameter in the control system is varied by the processing of the control system.
As shown in FIG. 15B, the angular range of the actual scan by the laser light (or the scan area) is set to be greater than the detection area in which reflected waves are received to obtain distance data (or the detection area in the standard scan direction) such that the position of the detection area can be adjusted in the scan direction to a certain degree by varying the set position (software parameter) in data processing within the scan area of this detection area (or within the area which allows detection or the detection-permitting area) without physically varying the position of attachment of the detection head of the device. The position of the aforementioned scan area and detection area may be wholly adjusted to a certain extent in the direction of the scan by varying the set software parameter value of the range of operation of the scan mechanism.
Japanese Patent Publication Tokkai 2000-75031 disclosed a method of adjustment without the shortcomings of the conventional methods shown by FIGS. 15A and 15B, being able to adjust in a short time both in the scan direction and the perpendicular direction by using a single target. Japanese Patent Publications Tokkai 11-326495, 11-64489 and 7-225277 disclosed technologies of axial adjustment of a radar in the horizontal or perpendicular direction. Japanese Patent Publication Tokkai 2002-74339 disclosed a method of setting a specified mark at the front end of one's own vehicle and using this mark to adjust the direction of a camera, and Japanese Patent Publication Tokkai 2000-142221 disclosed a method of adjustment by taking a specified image.
All of these prior art axial adjustment methods are for adjusting the position of the central axis of a detection area in two directions (such as the horizontal direction and the perpendicular direction) and no thought is given to the axial displacement in the direction of rolling. In the above, the axial displacement in the rolling direction means the rotational displacement of the detection area around an axis of rotation from the condition where the standard direction is horizontally oriented. For this reason, there was a possibility with conventional devices that there may result a significant distance between a monitored position and an actual position near the edge of a detection area (far from the center axis) even after an axial adjustment and that no sufficiently accurate measurement could be made. In the case of an ordinary radar installed on a vehicle as a single body and in particular in the case of a one-dimensional scan radar adapted to scan only in one direction (usually the horizontal direction) without regard to the perpendicular directions (such as the vertical direction), axial displacements in the rolling direction were of no importance because measurement errors in the perpendicular directions presented no problem. If the monitoring device is of a fusion type, employing a plurality of sensors (such as a radar and a camera), however, the merits of the fusion type cannot be fully utilized without taking into consideration a proper correlation between the results of measurement by the sensors. Thus, it is necessary to adjust the axial displacement in the rolling direction and to keep the axial displacement small in the rolling direction or to grasp the axial displacement and to keep it reflected in the position data.
The conventional methods of axial adjustment had problems in the case of a fusion type employing both a radar and a camera because different targets had to be used for axially adjusting the radar and the camera independently of each other. Firstly, if the conventional method of axial adjustment is applied to the fusion form, the relative positional relationship between the radar and the camera may become inappropriate due to errors in setting targets or marks for the adjustment (such that the axes of the detection areas of the sensors may not be parallel or the sensors may be tilted with respect to each other in the rolling direction. This is because the positional errors between the vehicle and the sensors are multiplied together. It is also because the axial displacement of each sensor is in an unadjusted condition and the orientations of the detection areas in the rolling direction do not match. If the relative positional relationship between the sensors becomes incorrect, correlation cannot be properly taken between the data recognized by the sensors of the fusion type and the advantage of the fusion type fails to be taken sufficiently.
Since the axial adjustments of the radar and the camera are made by using different targets, furthermore, the adjustment becomes complicated and time-consuming.